The present invention relates to an input data reader apparatus for a switch array (matrix) adapted to a touch panel or the like which is generally provided around the display location of a CRT (Cathode Ray Tube) display, an LCD (Liquid Crystal Display), etc.
A touch panel for manually inputting raw data is often provided at the front side of the display location of a CRT or LCD apparatus. Such a panel has a plurality (m x n) of switches arranged in a matrix fashion. Given drive signals are supplied to the matrix switches and the resultant logical output (sense signals) are derived from the matrix switches. The contents of inputted data of the touch panel or the combination of the depressed matrix switches are detected by an arithmetic logic unit (ALU) according to the sense signals. The detected contents of the inputted data are used thereafter for performing a prescribed operation.
In the manipulation of the matrix switches, two operation rules are generally applied. In the former rule, simultaneous depressing of two or more switches is inhibited. In the latter rule, simultaneous depressing of one or more switches in relation to the switching of another specific switch is allowed according to the specification or the function of the apparatus. For instance, in a process control performed by an operator's key board utilizing a touch panel, the former rule may be applied to a numerical input of 0 to 9 (ten-key input) or an alphabetic input, without any inconvenience. On the other hand, in a process control performed by a remote operation switch, two or more switches could be simultaneously depressed. In this case, the latter rule should be applied. Such simultaneous depressing may be done in a case wherein respective control target data for plural independent control loops should be inputted at the same time, or in a case wherein a plurality of key-input data (manipulation signals) should be outputted continuously. In order to correctly detect the combination of simultaneously depressed plural switches, signal leakages among the respective depressed switches should be eliminated. To eliminate such signal leakages, each of a conventional matrix switches is provided with a leakage-blocking diode as shown in FIG. 1.
FIG. 1 shows a conventional 3.times.3 switch matrix circuit having leakage-blocking diodes dj (j=1, 2, . . . , 9). In FIG. 1, series-circuit of switches si (i=1, 2, . . . , 9) and diodes dj are located at respective cross-points (nodes) of row (input) lines for drive signals D1 to D3 and column (output) lines for sense signals S1 to S3. The row lines receive drive signals D1 to D3, and column lines supply sense signals S1 to S3. When only the switches s1, s4 and s5 are turned on (depressed), the waveforms of drive signals D1 to D3 become as shown in FIGS. 2A to 2C and the waveforms of sense signals S1 to S3 become as shown in FIGS. 2D to 2F. According to the logical states of sense signals S1 to S3, an ALU (not shown) detects that the switches s1, s4 and s5 are depressed.
If diodes d1 to d9 are not provided in the circuit of FIG. 1, when switches s1, s2 and s4 are turned on, drive signal D2 leaks through the turned-on switches s1 and s2 to the column line of sense signal S2. Then, the said signal leakage occurs, and a correct detection of the combination of simultaneously depressed switches is disturbed.
From the above, if simultaneous depressing of two or more switches on the touch panel is not inhibited, diode dj cannot be deleted because of the signal leaking. In practice, however, it is difficut to mount the respective diodes dj closely to the switches si arranged on a touch panel. In such a case, the wiring for matrix switches si is not completed at the touch panel side. Rather, respective wirings of switches si are led out via independent contacts of a connector to the outside of the touch panel, and the matrix wiring is completed at the outside of the touch panel with the wiring of leakage-blocking diodes dj. This requires a large number of contacts in the connector and renders the matrix wiring with diodes dj complicated.